1. Field of the Invention
The present invention concerns a gantry for a computed tomography apparatus of the type having an outer supporting body and a support ring that supports a rotary carriage, the support ring and the supporting body forming a cooling channel for supply of a coolant to the rotating rotary carriage.
2. Description of the Prior Art
In a computed tomography apparatus, three-dimensional slice images of the inside of a patient are generated by x-ray irradiation. For this purpose, two-dimensional x-ray slice images, from which a three-dimensional slice image is reconstructed, are generated by a scanning unit that normally has an x-ray radiator rotating around the subject and an image acquisition system. The tomography apparatus typically has a stationary part with a support ring that is arranged around a patient acquisition space and a supporting body for the support ring. A rotatable rotary carriage that includes the x-ray radiator and an oppositely-situated x-ray detector is mounted on the support ring. The rotary carriage together with the stationary part is typically called a gantry.
A problem in such a computed tomography apparatus is the dissipation of heat that accumulates in the x-ray radiator and the x-ray detector because 99% of the energy used to generate x-rays is converted into heat. Local air cooling, for example by means of a ventilator, cannot be used or can be used only in a limited manner in a tomography apparatus. The supply and discharge of a gaseous or liquid coolant by means of rigid or flexible coolant lines cannot be realized or can be realized only in a complicated manner, because of the difficulty of configuring such lines so that they do not hinder the required rotation movement capability of the rotary carriage.
Cooling systems conventionally used in such tomography apparatus generally include a number of heat exchangers that are installed inside the support ring. In order to efficiently dissipate heat accumulating at the rotating x-ray radiator from the inside of the rotary carriage, a heat exchanger that rotates with the rotary carriage is conventionally mounted in the immediate proximity of the x-ray radiator. This first heat exchanger emits the heat to the surrounding air. The heated air can be cooled, for example, by a second heat exchanger that dissipates the heat acquired from the air to a cooling system outside of the support ring.
For example, DE 199 45 413 A1 describes a computed tomography apparatus in which the second heat exchanger is mounted stationary relative to the x-ray radiator. The heat absorbed during the operation is dissipated to a cooling system outside of the support ring via coolant lines arranged in a second heat exchanger. It has proven to be disadvantageous that a number of precise mechanical and electrical components are necessary in this arrangement that tend to wear (due to their function) and must be correspondingly serviced. A further disadvantage is in that the gantry must be dimensioned with a relatively large volume due to the size of the heat exchanger required.
An alternative embodiment of a gantry of the type initially described, in which a number of heat exchangers are foregone, is disclosed in PCT Application WO 2005/048843. The computed tomography apparatus according to this publication has a support frame (load-bearing structure) that is fashioned as a hollow section and on which a support ring is attached. The hollow channels that are formed inside the support frame serve for supply and discharge of a coolant.
A problem with this arrangement is an impairment of the stability of the apparatus because the support ring is supported on only one footing formed by two horizontal struts, and a base plate with a series of cavities.